RPC method

eth_chainId on Sei

Supported on SwiftNodes

Everything below was measured on 2026-10-13 by calling eth_chainId on Sei through the same endpoint customers use, and is re-measured weekly.

What eth_chainId does

Returns the chain ID (EIP-155) as a hex string. Wallets and libraries check it before signing, and the signature commits to it, so a transaction signed for one chain cannot be replayed on another.

Sei chain ID, as measured

net_version returns the same number as decimal text. Older tools read net_version; use eth_chainId, which is the value signatures commit to.

We sent Sei a legacy transaction signed without a chain ID (pre-EIP-155). Its nodes refused it: ": unknown". Sign with chain ID 1329; every mainstream library does this by default.

eth_chainId	0x531 (1,329)
net_version	1329

Example request

curl -s https://rpc.swiftnodes.io/rpc/sei?key=YOUR_API_KEY \
  -X POST -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"eth_chainId","params":[]}'

// Check you are on Sei before signing
import { createPublicClient, http } from "viem";

const client = createPublicClient({
  transport: http("https://rpc.swiftnodes.io/rpc/sei?key=YOUR_API_KEY"),
});

const id = await client.getChainId(); // 1329
if (id !== 1329) throw new Error(`wrong chain: ${id}`);

// Add Sei to a browser wallet
await window.ethereum.request({
  method: "wallet_addEthereumChain",
  params: [{
    chainId: "0x531",
    chainName: "Sei",
    nativeCurrency: { name: "SEI", symbol: "SEI", decimals: 18 },
    rpcUrls: ["https://rpc.swiftnodes.io/rpc/sei?key=YOUR_API_KEY"],
  }],
});

Other methods on Sei

eth_chainId on other chains

Frequently asked questions

Does Sei support eth_chainId?

Yes. eth_chainId answered on the SwiftNodes Sei endpoint when our weekly probe called it through the customer path (2026-10-13).

What is the Sei chain ID?

1329 in decimal, 0x531 in hex, as returned by eth_chainId on 2026-10-13.

How do I add Sei to MetaMask?

Call wallet_addEthereumChain with chainId 0x531, the native currency SEI with 18 decimals, and your RPC URL; the example on this page has the full object.

Sei endpoints, live block height and WebSocket status are on the Sei RPC page.

One key covers every chain we serve, and SwiftNodes has a free tier.